Method for the treatment of Dravet syndrome

ABSTRACT

A method of treating and/or preventing Dravet Syndrome in a patient such as a patient previously diagnosed with Dravet Syndrome, by administering an effective dose of fenfluramine or its pharmaceutically acceptable salt to that patient. Dravet Syndrome patients are typically children under the age of 18 and are treated at a preferred dose of less than about 0.5 to about 0.01 mg/kg/day.

BACKGROUND ART

This invention relates to the treatment of Dravet Syndrome using anamphetamine derivative, specifically fenfluramine.

Fenfluramine, i.e. 3-trifluoromethyl-N-ethylamphetamine is anamphetamine derivative having the structure:

Fenfluramine was first marketed in the US in 1973 and had beenadministered in combination with phentermine to prevent and treatobesity. However, in 1997, it was withdrawn from the US market as itsuse was associated with the onset of cardiac fibrosis and pulmonaryhypertension. Subsequently, the drug was withdrawn from sale globallyand is no longer indicated for use in any therapeutic area.

Despite the health concerns surrounding fenfluramine, attempts have beenmade to identify further therapeutic uses for that product. Aicardi andGastaut (New England Journal of Medicine (1985), 313:1419 and Archivesof Neurology (1988) 45:923-925) reported four cases of self-inducedphotosensitive seizures that responded to treatment with fenfluramine.

Clemens, in Epilepsy Research (1988) 2:340-343 reported a study on a boysuffering pattern sensitivity-induced seizures that were resistant toanticonvulsive treatment. Fenfluramine reportedly successfullyterminated these self-induced seizures and the author concluded thatthis was because fenfluramine blocked the photosensitive triggeringmechanism.

In Neuropaediatrics, (1996); 27(4):171-173, Boel and Casaer reported ona study on the effects of fenfluramine on children with refractoryepilepsy. They concluded that when fenfluramine was administered at adose of 0.5 to 1 mg/kg/day, this resulted in a reduction in the numberof seizures experienced by the patients.

In a letter to Epilepsia, published in that journal (Epilepsia,43(2):205-206, 2002), Boel and Casaer commented that fenfluramineappeared to be of therapeutic benefit in patients with intractableepilepsy.

Epilepsy is a condition of the brain marked by a susceptibility torecurrent seizures. There are numerous causes of epilepsy including, butnot limited to birth trauma, perinatal infection, anoxia, infectiousdiseases, ingestion of toxins, tumours of the brain, inherited disordersor degenerative disease, head injury or trauma, metabolic disorders,cerebrovascular accident and alcohol withdrawal.

There are a large number of subtypes of epilepsy that have beencharacterised. For example, the following list of conditions are set outin Meritt's Neurology (12th Edition):

I. Idiopathic epilepsy syndromes (focal or generalised)

-   -   A. Benign neonatal convulsions        -   1. Familial        -   2. Nonfamilial    -   B. Benign childhood epilepsy        -   1. With central-midtemporal spikes        -   2. With occipital spikes    -   C. Childhood/juvenile absence epilepsy    -   D. Juvenile myoclonic epilepsy (including generalised        tonic-clonic seizures on awakening)    -   E. Idiopathic epilepsy, otherwise unspecified        II. Symptomatic epilepsy syndromes (focal or generalised)    -   A. West syndrome (infantile spasms)    -   B. Lennox-Gastaut syndrome    -   C. Early myoclonic encephalopathy    -   D. Epilepsia partialis continua        1. Rasmussen syndrome (encephalitic form)        2. Restricted form    -   E. Acquired epileptic aphasia (Landau-Kleffner syndrome)    -   F. Temporal lobe epilepsy    -   G. Frontal lobe epilepsy    -   H. Posttraumatic epilepsy    -   I. Other symptomatic epilepsy, focal or generalised, not        specified        III. Other epilepsy syndromes of uncertain or mixed        classification    -   A. Neonatal seizures    -   B. Febrile seizures    -   C. Reflex epilepsy    -   D. Other unspecified

As can be seen from, for example, Part III of that list, there are stillsubtypes of epilepsy that have not yet been fully characterized andthus, the list is far from complete.

Those skilled in the art will recognize that these subtypes of epilepsyare triggered by different stimuli, are controlled by differentbiological pathways and have different causes, whether genetic orenvironmental. In other words, the skilled artisan will recognize thatteachings relating to one epileptic subtype are not necessarily beapplicable to other subtypes. This can include recognition thatdifferent epilepsy subtypes respond differently to differentanticonvulsant drugs.

Dravet Syndrome is a rare and catastrophic form of intractable epilepsythat begins in infancy. Initially, the patient experiences prolongedseizures. In their second year, additional types of seizure begin tooccur and this typically coincides with a developmental decline,possibly due to repeated cerebral hypoxia. This leads to poordevelopment of language and motor skills.

Children with Dravet Syndrome are likely to experience multiple seizuresper day. Epileptic seizures are far more likely to result in death insufferers of Dravet Syndrome; approximately 10 to 15% of patientsdiagnosed with Dravet Syndrome die in childhood, particularly betweentwo and four years of age. Additionally, patients are at risk ofnumerous associated conditions including orthopedic developmentalissues, impaired growth and chronic infections.

Of particular concern, children with Dravet Syndrome are particularlysusceptible to episodes of Status Epilepicus. This severe andintractable condition is categorized as a medical emergency requiringimmediate medical intervention, typically involving hosptialisation.Status Epilepticus can be fatal. It can also be associated with cerebralhypoxia, possibly leading to damage to brain tissue. Frequenthospitalizations of children with Dravet Syndrome are clearlydistressing, not only to the patient but also to family and carers.

The cost of care for Dravet Syndrome patients is also high as theaffected children require constant supervision and many requireinstitutionalisation as they reach teenage years.

At present, although a number of anticonvulsant therapies can beemployed to reduce the instance of seizures in patients with DravetSyndrome, the results obtained with such therapies are typically poorand those therapies only effect partial cessation of seizures at best.Seizures associated with Dravet Syndrome are typically resistant toconventional treatments. Further, many anticonvulsants such as clobazamand clonazepam have undesirable side effects, which are particularlyacute in pediatric patients.

Stiripentol is approved in Europe but not in the US for the treatment ofDravet Syndrome. It does not exhibit an anticonvulsant activity in itsown right; it acts by inhibiting the metabolism of other anticonvulsantsthereby prolonging their activity. However, concerns remain regardingthe use of stiripentol due to its inhibitory effect on hepaticcytochrome P450. Further, the interactions of stiripentol with a largenumber of drugs means that combination therapy (which is typicallyrequired for patients with Dravet Syndrome) is problematic.

There is accordingly a need to provide an improved method for treatingor preventing Dravet Syndrome and/or for treating, preventing and/orameliorating seizures experienced by sufferers of Dravet Syndrome.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method of treating and/or preventing Dravet Syndrome in a patientcomprising administering an effective dose of fenfluramine to thatpatient.

According to a further aspect of the present invention, there isprovided a method of treating, preventing and/or ameliorating seizuresin a patient diagnosed with Dravet Syndrome comprising administering aneffective dose of fenfluramine to that patient.

According to a further aspect of the present invention, there isprovided a method of treating a patient that exhibits a mutation in oneor more of a gene selected from the group consisting of SCN1A, SCN1B,SCN2A, SCN3A, SCN9A, GABRG2, GABRD and PCDH19 by by administering tothat patient an effective dose of fenfluramine.

A still further aspect of this invention contemplates a method forstimulating one or more 5-HT receptors in the brain of a patient byadministering an effective dose of fenfluramine or a pharmaceuticallyacceptable salt thereof to that patient. Illustrative one or more 5-HTreceptors are selected from the group consisting of one or more of5-HT₁, 5-HT_(1A), 5-HT_(1B), 5-HT_(1C), 5-HT_(1D), 5-HT_(1E), 5-HT_(1F),5-HT₂, 5-HT_(2A), 5-HT_(2B), 5-HT_(2C), 5-HT₃, 5-HT₄, 5-HT₅, 5-HT_(5A),5-HT_(5B) 5-HT₆, and 5-HT₇.

Yet another aspect of the invention contemplates coadministration of aneffective dose of one or more co-therapeutic agents with thefenfluramine.

DETAILED DESCRIPTION OF THE INVENTION

After many years of extensive research, it has unexpectedly been foundthat fenfluramine can be used to treat, or at least minimiZe the effectsof Dravet Syndrome. This is confirmed by the results presented herein,and also in the article by Ceulemans et al., Epilepsia (2012)53(7):1131-1139, the contents of which are incorporated herein.

For the avoidance of doubt, the term “prevention” of seizures means thetotal or partial prevention (inhibition) of seizures. Ideally, themethods of the present invention result in a total prevention ofseizures; indeed, this ideal has been achieved in a number of patientstreated by the inventors. However, the invention also encompassesmethods in which the instances of seizures are decreased by at least50%, at least 60%, at least 70%, at least 80% or at least 90%.

It is known that patients with Dravet Syndrome commonly experiencephotosensitive or induced seizures. From teachings in the prior art,e.g. Aicardi and Gastaut (1988) and Boel and Casaer (1996)—bothdiscussed above, it might have been expected that fenfluramine wouldreduce photosensitive or induced seizures. Importantly, however, it hassurprisingly been found that all types of seizures exhibited by patientswith Dravet Syndrome, that is seizures in addition to and other thanthose that are photosensitive or induced can be suppressed by treatmentin accordance with a method of the present invention.

Thus, in context of the present invention, the term “seizure” is used tonot only encompass photosensitive or induced seizures, but some or allof the other types of seizures experienced by epileptics, including butnot limited to Status Epilepticus.

There are a number of genetic mutations that are indicative of DravetSyndrome. Mutations in the SCN1A (such as partial or total deletionmutations, truncating mutations and/or missense mutations e.g. in thevoltage or pore regions S4 to S6), SCN1B (such as the region encodingthe sodium channel β1 subunit), SCN2A, SCN3A, SCN9A, GABRG2 (such as theregion encoding the γ2 subunit), GABRD (such as the region encoding theδ subunit) and/or PCDH19 genes have been linked to Dravet Syndrome.

Thus, according to a further aspect of the present invention, there isprovided a method of treating a patient that exhibits a mutation in one,some or all of the above genes by administering to that patient aneffective dose of fenfluramine. In certain embodiments of this aspect ofthe invention, the patient has been diagnosed with Dravet Syndrome.

Fenfluramine has been known to inhibit serotonin reuptake and to triggerthe release of serotonin in the brain due to disruption of its vesicularstorage. However, until the present invention was made, it was not knownthat fenfluramine's mechanism of action made it suitable for thetreatment of Dravet Syndrome.

Thus, according to a still further aspect of the present invention,there is provided a method of stimulating one or more 5-HT receptors inthe brain of a patient by administering an effective dose offenfluramine to said patient, said one or more 5-HT receptors beingselected from one or more of 5-HT₁, 5-HT_(1A), 5-HT_(B), 5-HT_(1D),5-HT_(1E), 5-HT₂, 5-HT_(2A), 5-HT_(2B), 5-HT_(2C), 5-HT₃, 5-HT₄, 5-HT₅,5-HT_(5A), 5-HT_(5B) 5-HT₆, and 5-HT₇ amongst others. In certainembodiments of this aspect of the invention, the patient has beendiagnosed with Dravet Syndrome.

In embodiments of the invention, any effective dose of fenfluramine canbe employed. However, surprisingly low doses of fenfluramine have beenfound by the inventors to be efficacious, particularly for inhibiting oreliminating seizures in Dravet Syndrome patients. Thus, in preferredembodiments of the invention, a daily dose of less than about 0.5mg/kg/day, about 0.45 mg/kg/day, about 0.4 mg/kg/day, about 0.3mg/kg/day, about 0.25 mg/kg/day or about 0.2 mg/kg/day to about 0.1mg/kg/day, about 0.05 mg/kg/day, or about 0.01 mg/kg/day is employed.Put differently, a preferred dose is less than about 0.5 to about 0.01mg/kg/day. Such a dose is less than the daily dose of fenfluraminesuggested for administration to achieve weight loss.

The dose of fenfluramine administered in the methods of the presentinvention can be formulated in any pharmaceutically acceptable dosageform including, but not limited to oral dosage forms such as tabletsincluding orally disintegrating tablets, capsules, lozenges, oralsolutions or syrups, oral emulsions, oral gels, oral films, buccalliquids, powder e.g. for suspension, and the like; injectable dosageforms; transdermal dosage forms such as transdermal patches, ointments,creams; inhaled dosage forms; and/or nasally, rectally, vaginallyadministered dosage forms. Such dosage forms can be formulated for oncea day administration, or for multiple daily administrations (e.g. 2, 3or 4 times a day administration).

The dosage form of fenfluramine employed in the methods of the presentinvention can be prepared by combining fenfluramine with one or morepharmaceutically acceptable diluents, carriers, adjuvants, and the likein a manner known to those skilled in the art of pharmaceuticalformulation.

In a method of the present invention, fenfluramine can be employed as amonotherapy in the treatment of Dravet Syndrome. Alternatively,fenfluramine can be coadministered simultaneously, sequentially orseparately with one or more co-therapeutic agents, such asanticonvulsants. Preferred co-therapeutic agents can be selected fromthe group consisting of carbamazepine, ethosuximide, fosphenytoin,lamotrigine, levetiracetam, phenobarbitol, progabide, topiramate,stiripentol, valproic acid, valproate, verapamil, and benzodiazepinessuch as clobazam, clonazepam, diazepam, ethyl loflazepate, lorazepam,midazolam. Use of a pharmaceutically acceptable salt of a co-therapeuticagent is also contemplated.

Fenfluramine can be administered in the form of the free base, or in theform of a pharmaceutically acceptable salt, for example selected fromthe group consisting of hydrochloride, hydrobromide, hydroiodide,maleate, sulphate, tartrate, acetate, citrate, tosylate, succinate,mesylate and besylate. Further illustrative pharmaceutically acceptablesalts can be found in Berge et al., J. Pharm Sci. (1977) 68(1):1-19.

Fenfluramine for use in the methods of the present invention may beproduced according to any pharmaceutically acceptable process known tothose skilled in the art. Examples of processes for synthesizingfenfluramine are provided in the following documents: GB1413070,GB1413078 and EP441160.

The dose of fenfluramine to be used in a method of the present inventioncan be provided in the form of a kit, including instructions for usingthe dose in one or more of the methods of the present invention. Incertain embodiments, the kit can additionally comprise a dosage formcomprising one or more co-therapeutic agents.

A method of the present invention can be practiced on any appropriatelydiagnosed patient. In a typical embodiment of the present invention, thepatient is aged about 18 or less, about 16 or less, about 14 or less,about 12 or less, about 10 or less, about 8 or less, about 6 or less orabout 4 or less to about 0 months or more, about 1 month or more, about2 months or more, about 4 months or more, about 6 months or more orabout 1 year or more. Thus, the diagnosed patient is typically about onemonth old to about 18 years old when treated.

The invention is further illustrated in the following ComparativeExample.

Comparative Example 1

The results of two pivotal studies (conducted in France and Italy) thatled to approval of stiripentol in the European Union are provided below.In the first table, the number of test subjects who became seizure-freeupon co-administration of stiripentol and either valproate or clobazamvs a placebo or two months is provided. In the second table, the numberof subjects who exhibited a >50% reduction in the number of seizuresfollowing administration of stiripentol and either valproate or clobazamvs a placebo or two months is provided.

TABLE 1 Seizure Free Patients (Treated with Stiripentol and eitherValproate or Clobazam vs Placebo) Seizure Free Patients StiripentolPlacebo STICLO-France 9/20 (45%) 0/16 (0%) STICLO-Italy 3/11 (27%)  0/9(0%) Combined  12/31 (38.7%) 0/25 (0%)

TABLE 2 Responders - >50% Reduction in the Number of Seizures (Treatedwith Stiripentol and either Valproate or Clobazam vs Placebo) RespondersStiripentol Placebo STICLO-France 15/21 (71.4%) 1/20 (5%)   STICLO-Italy 8/12 (66.7%) 1/11 (9.1%) Combined 23/33 (69.7%) 2/31 (6.5%)

The following table provides results based on the data presented inCeulemans et al., Epilepsia (2012) 53(7):1131-1139. Patients wereadministered an average daily dose of fenfluramine of 0.34 mg/kg/day forbetween 1 and 22 years.

TABLE 3 Seizure Free Patients and Responders (Treated with Fenfluramineand Valproate) Fenfluramine Seizure-free Patients >50% Reduction inSeizures 8/12 (66%) 9/12 (75%)As can be seen from the foregoing data, long-term fenfluramine treatmentadvantageously resulted in a seizure-free condition in 66.6% of testsubjects, compared to 38.7% for stiripentol.

Additionally, long-term fenfluramine treatment advantageously resultedin a slightly improved reduction in seizures (75%) as compared to thereduction in seizures in patients treated with stiripentol for twomonths (69.7%).

These results confirm that fenfluramine provides long termelimination/reduction in seizures to a greater extent than observed withshort term administration of the currently approved therapy (in the EU),stiripentol.

These results were achieved, in the vast number of cases, usingsignificantly lower doses of fenfluramine than those proposed previouslyin the treatment of various conditions typified by seizures.Additionally and surprisingly, fenfluramine effectively reduced theincidence of all types of seizures and not only photosensitive orself-induced seizures.

The subjects treated with fenfluramine were monitored usingechocardiography for possible heart valve defects. No clinicallyrelevant defects were identified.

Each of the patents, patent applications and articles cited herein isincorporated by reference. The use of the article “a” or “an” isintended to include one or more.

The foregoing description and the examples are intended as illustrativeand are not to be taken as limiting. Still other variations within thespirit and scope of this invention are possible and will readily presentthemselves to those skilled in the art.

The invention claimed is:
 1. A method of stimulating 5-HT receptors inthe brain of a patient diagnosed with Dravet syndrome, comprising:administering to the patient 0.2 mg/kg/day of fenfluramine or apharmaceutically acceptable salt thereof; and administering to thepatient an effective dose of stiripentol or a pharmaceuticallyacceptable salt thereof; whereby 5-HT receptors are stimulated andwherein the 5-HT receptor is in a family of receptors selected from thegroup consisting of 5-HT1, 5-HT2, 5-HT3, 5-HT4, 5-HT5, 5-HT6, and 5-HT7.2. The method of claim 1, wherein the 5-HT receptor is in the 5-HT1receptor family and is selected from the group consisting of 5-HT1A,5-HT1B, 5-HT1C, 5-HT1D, 5-HT1E, 5-HT1F.
 3. The method of claim 1,wherein the 5-HT receptor is in the 5-HT2 receptor family and isselected from the group consisting of 5-HT2A, 5-HT2B, 5-HT2C.
 4. Themethod of claim 1, wherein the 5-HT receptor is the 5-HT3 receptor.
 5. Amethod of stimulating 5-HT receptors in the brain of a patient diagnosedwith Dravet syndrome, comprising: administering to the patient aneffective dose of fenfluramine or a pharmaceutically acceptable saltthereof administered in a dose of 0.5 mg/kg/day to 0.2 mg/kg/day to thepatient; and administering to the patient an effective dose ofstiripentol or a pharmaceutically acceptable salt thereof; whereby 5-HTreceptors are stimulated.
 6. The method of claim 5, wherein theeffective dose is administered in the form of one or more dosage formsfor oral, injectable, transdermal, inhaled, nasal, rectal, vaginal orparenteral delivery.